1. Technical Field of the Invention
The present invention relates to an X-ray CT system for performing a scan using an cone-like X-ray beam, and in particular, to an X-ray CT system, which is also called cone-beam CT system, that is able to acquire two-dimensional projection data of transmitted X-rays using a two-dimensional detector and obtain CT images by applying three-dimensional reconstruction to the two-dimensional projection data.
2. Related Art
An X-ray CT scanner is provided a gantry in which both of an X-ray tube (X-ray radiation device) and an X-ray detector are disposed to make an object locate therebetween. For example, when an R-R driving technique is adopted, both the X-ray tube and the X-ray detector are driven in synchronism with each other to be rotated about the object, and X-ray beams radiated from the X-ray tube are made to enter the X-ray detector through the object. A DAS (data acquisition system) is connected to the X-ray detector, so that data indicative of intensity of projected X-rays is acquired by the DAS for every scan. Reconstructing the acquired projection data produces internal image data of the object (i.e., slice data or volume data).
In the field of such an X-ray CT scanner, in recent years, CT that involves scanning based on a cone beam, that is, cone-beam CT has been studied eagerly, as one approach to fast producing three-dimensional images of higher resolution.
For example, a Japanese Patent Laid-open publication No. HEI 9-19425 proposes an X-ray computer tomography imaging system serves as a cone-beam CT scanner, wherein error in reconstruction, which is attributable to shifts between an actually-measured X-ray path and a computed X-ray path, is relieved to improve image quality.
In addition, another Japanese Patent Laid-open publication No. 2000-102532 proposes an X-ray CT scanner serving as a cone-beam CT scanner, which is able to accurately acquire projection data of high resolution by performing a scan using a cone beam produced from continuous X-rays. This acquisition is achieved, with the circuitry of DAS kept to a practical size, without prolonging a scan time, and with a less effective path even when shifts occur in acquisition timing of projection data.
However, if the above-listed conventional cone-beam CT scanners are desired to be used as an actual CT scanner, such CT scanners will encounter problems resulted from the fact that an object, that is, a patient may move during a scan. That is, when a universal three-dimensional reconstruction algorithm is applied to projection data to obtain images, without taking the object motion into consideration, artifacts arise on the images and temporal resolution deteriorates.